Hitherto, nonwoven fabrics have been widely used as material for sanitary materials, general household supplies, and industrial supplies. Materials used as constituent fibers of such fabrics include, for example, polymers such as polyethylene, polypropylene, polyester, and polyamide. However, it must be pointed out that nonwoven fabrics made of such material are not self-degradable and are chemically very stable under normal environmental conditions. Therefore, it has been general practice that disposable type nonwoven fabrics, after use, are disposed by such a method as incineration or landfill disposal. In Japan, disposal by incineration is widely in practice which, however, involves great expenditure and results in environmental pollution due to waste plastics. Indeed, how to solve the problem of waste plastics disposal is becoming an object of great public concern from the standpoints of nature conservation and living-environment protection. Landfill disposal involves a problem that the waste will long remain unchanged in the ground from its original state because the material thereof is chemically stable.
In order to solve such a problem, it has been desired to produce a novel nonwoven fabric which is made from a degradable (i.e., microbially degradable or biodegradable) material and can be naturally degraded in a short time period.
Typically, examples of biodegradable fibers include cellulose fibers represented by cotton and linen and protein fibers represented by silk. Since these natural fibers are non-thermoplastic, however, it is impracticable to employ the so-called embossing technique or thermal bond technique in which fibers are thermally bonded together into a nonwoven fabric, for purposes of fabricating a nonwoven fabric from any such natural fiber. Any nonwoven fabric made from a natural fiber material would not become degraded in a short period of time and would continue to exist in its form as such. This is undesirable when considered in the interests of nature conservation and living-environment protection.
Biodegradable polymers are well known including polysaccharides, such as chitin; proteins, such as catgut and regenerated collagen; polypeptide (polyamino acid); microbial polyesters, such as poly-3-hydroxybutyrate, poly-3-hydroxyvalylate, and poly-3-hydroxycaprolate, which are microbially produced in nature; and synthetic aliphatic polyesters, such as polyglycolide and polylactide. However, producing fibers of these polymers involves the limitation that the wet spinning technique be employed. Further, such fibers are very costly and this limits the applicability for use of the fibers to such a particular field as bioabsorbable sutures.
Recently, a biodegradable film has been proposed which comprises a blend of polyethylene and starch. Such a film is now used as material for shopping bags. However, this type of film cannot be said to be a biodegradable film in a primary sense of the term, because polyethylene will permanently remain undegraded. Indeed, it is no easy task to produce a fiber of such a blend which is applicable for use in fabricating a nonwoven fabric; and to date no starch-containing fiber has been proposed for production of nonwoven fabrics.